The present invention relates generally to gas turbines and more particularly relates to cooling air circuits within a turbine airfoil.
Generally described, gas turbine buckets may have airfoil shaped body portions. The buckets may be connected at their inner ends to root portions and connected at their outer ends to tip portions. The buckets also may incorporate shrouds at these tip portions. Each shroud cooperates with like elements on adjacent buckets to prevent hot gas leakage past the tips. The use of the shrouds also may reduce vibrations.
The tip shrouds, however, may be subject to creep damage age due to the combination of high temperatures and centrifugally induced bending stresses. One method of cooling each bucket as a whole is to use a number of cooling holes. The cooling holes may transport cooling air through the bucket and form a thermal barrier between the bucket and the flow of hot gases.
Although cooling the buckets may reduce creep damage, the use of cooling air to cool the bucket may reduce the efficiency of the gas turbine as a whole due to the fact that this cooling air is not passing through the turbine section. The cooling air flow therefore should be at a minimum speed for the part. Likewise, the cooling holes may require optimization of the hole location, size, and style.
What is desired, therefore, is a cooling hole scheme for a turbine bucket that limits the reduction in overall system efficiency while providing adequate cooling to prevent creep. The scheme preferably also should increase part life.